1. Field of the Invention
This invention pertains to improvements in motor driving and controlling circuitry, and more particularly, to an improved circuit and method for detecting overtemperature conditions of the substrate on which motor driver circuitry is fabricated.
2. Technical Background
The present invention pertains to polyphase dc motors, and particularly to brushless, sensorless polyphase dc motors which are used for rotating data media, such as found in computer related applications, including hard disk drives, CD ROM drives, floppy disks, and the like. In computer applications, three phase brushless, sensorless dc motors are becoming more popular, due to their reliability, low weight, and accuracy.
Motors of this type can typically be thought of as having a stator with three coils connected in a "Y" configuration, although actually, a larger number of stator coils are usually employed with multiple motor poles. In operation, the coils are energized in sequences in which current paths are established through various coils combinations, in, for instance, six commutation sequences.
Typically, the driver transistors that supply the driving current to the coils of the motor are integrated onto a semiconductor substrate, as a part of an overall driver circuit. It will be appreciated, however, that substantial currents may flow in the drive transistors, as well as flyback energy from the coils being dissipated in the transistors, or associated diode elements. This results in heat being delivered to the substrate that must be dissipated to avoid damage to the circuit. Nevertheless, under certain conditions, the substrate may be heated to an undesirable level, requiring complete shut down of the circuit to avoid permanant damage.
In the past, temperature sensing has typically been used in motor driver circuits as a part of a shut down function. When an overtemperature condition occurred, it was detected and all of the operations of the driver circuit were immediately discontinued. In many instances, however, it might be possible to control the substrate temperature to prevent its reaching the critical shut down temperature, and the inconveniences resulting from complete circuit shut-down.